The present invention relates generally to electrical string musical instruments, and more specifically, to an improved signal processing circuit for the strings to emulate acoustic string musical instruments.
Musical instruments, for example, electric guitars, have a number of strings, connected between a bridge on the body and tuning pegs at the headstock. The vibration of the strings are sensed by transducers or pickups which are then signal processed and amplified. Typically, one or more transducers pick up the signal of all the strings simultaneously and provide a mono or single output of the combined signals. It has been known also to provide an individual transducer for each string and then combine the signals at a single mono output. The transducers are generally inductor coils. Depending on the location and type of transducer, the transducers do not sense the same vibrations as an acoustic instrument.
Instead of providing individual coils to pick up the signal of the individual strings, the use of individual piezoelectric transducers at the bridge have been used to pick up the signals from the individual strings. The signals again have been combined in a signal processing circuit to provide a mono output.
The signal processing of individual pickup from a string instrument to produce harmonic overtones and undertones are described in U.S. Pat. Nos. 3,213,180 and 5,218,160. Examples of individual signal processors for individual pickups for each string with signal modification to produce effects are described in U.S. Pat. No. 3,813,473, U.S. Pat. No. 4,357,852, Japanese Patent 6-110464 dated Apr. 22, 1994 and WO 87/00331. In U.S. Pat. No. 3,813,473, the effects to be produced are sustained-note effect, removal of sympathetic vibrations among strings and removal of the initial click sound produced by the plucking of the string. In U.S. Pat. No. 4,357,852, it uses a voltage controlled variable bandpass filter to follow and extract the fundamental in the guitar sound for each string. The extracted fundamental is then modulated with an envelope signal for synthesizing. In the Japanese Patent 6-110464, the effects are distortion and ululation. WO 87/00331 includes effects devices, such as reverberation, flanger and echo or delay devices. A compensation circuit for piezoelectric pickups in musical instruments is described in U.S. Pat. No. 5,877,447.
The present invention is a signal processing circuit for musical instruments, the musical instrument having a plurality of strings individually tuned to a frequency ranging from an open string to a fretted string. A signal processing circuit is provided for each string and includes a transducer adjacent to the string and an equalizer connected to an output circuit. The equalizer is set to emphasize signals present in a frequency range of the tuned frequency range of the respective string. The set frequency range of the equalizer may be the fundamental and/or one or more of the harmonics of the fundamentals of the individual string. Also, the equalizer de-emphasizes at least the low end frequency below the operating range for that string. The resulting or output signal emulates an acoustic instrument of the same type of instrument.
A mid-range frequency device is provided in the equalizer to produce characteristic mid-range response for a specific acoustic instrument. If the equalizer includes a digital signal processor, it can determine the frequency of the string and emphasize the determined frequency and its harmonics.
The stringed musical instrument can be selected from any string musical instrument, for example guitars, basses, mandolins, violins and cellos, pianos, harps, etc. Where the string instrument is a six stringed guitar, for example, the equalizers for the respective strings emphasize the tuned range of frequency of the fundamental, which can be one octave. For a bass, the equalizer for the respective string emphasizes one or more of the fundamental frequency and/or one or more of its harmonics within the tuned frequency range of the respective string.
Wherein the transducer is a piezoelectric transducer which contacts the string, the equalizer also de-emphasizes inherent resonance produced by the piezoelectric transducer. Where the stringed instrument includes a bridge supporting the strings, the transducers may be provided on the bridge. If other forms of transducers produce an inherent resonance at a characteristic frequency, the equalizer will also de-emphasize the inherent resonance produced by the transducer at the characteristic frequency of the transducer. A filter is used to de-emphasize the inherent resonance produced by the transducer at its characteristic frequency. For example, for piezoelectric transducers, the de-emphasized the inherent resonance is in the 6000-12000 hertz range.
The portion of the signal processing circuit which de-emphasizes the inherent resonance produced by the transducer may be in each equalizer for the strings. Alternatively, a single de-emphasizing circuit may be provided where a mono output is used. If a stereo output is used, a pair of circuits to de-emphasize the characteristic resonance of the transducer would be used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.